Preparation and characterization of poly(3-octylthiophene)/carbon fiber thermoelectric composite materials

Poly(3-alkylthiophene) (P3AT) with a high Seebeck coefficient has recently been reported. However, P3AT/inorganic conductive composites exhibit relatively poor thermoelectric performance because of their low electrical conductivity. In this work, carbon fiber sheets with a high electrical conductivity were chosen as the inorganic phase, and poly(3-octylthiophene)(P3OT)/carbon fiber composites were prepared by casting P3OT solution onto the carbon fiber sheets. The carbon fiber sheets incorporated into the composites can provide good electrical conductivity, and P3OT can provide a high Seebeck coefficient. The highest power factor of 7.05 μW m⁻¹ K⁻² was obtained for the composite with 50 wt% P3OT. This work suggests a promising method for preparing large-scale thermoelectric composites with excellent properties.     

同沙水库水环境质量的模糊数学综合评价

为选择合理的模型并充分地利用有限的监测数据,客观地描述环境质量优劣状况,为环境整体规划及环境污染防治提供依据,运用模糊数学方法,选用溶解氧、五日生化需氧量、化学需氧量、总磷、氨氮作为评价因子,参照地表水环境质量标准,通过计算污染因子权重、权重分配系数和隶属度对同沙水库水环境质量进行评价.3种模型计算结果均表明,同沙水库...     

Electrochemical properties and thermal neutral state of solid oxide fuel cells with direct internal reforming of methane

Solid oxide fuel cells (SOFCs) with direct internal reforming (DIR) provide a promising method to realize clean and efficient utilization of hydrocarbon fuels. Thse endothermic reforming reactions occur simultaneously with exothermic electrochemical reactions at the anode, making thermal neutral state achievable inside a fuel cell, providing reference to the thermal management. In this study, a calculation model combining experimental data and thermodynamic results was established, validating the possibility of achieving thermal neutral state in DIR-SOFCs. In the process of modeling, the electrochemical and thermodynamic characteristics in direct internal steam and dry reforming were elaborately compared, contributing to a more scientific understanding of anode reaction mechanism. Detailed experimental investigation was carried out to determine the influence of H₂O/CO₂ on the electrochemical properties of DIR-SOFCs, based on which the optimum steam-carbon ratio (S/C) and CO₂ to CH₄ ratios were obtained. Besides, analysis of distribution of relaxation times (DRT) combined with elementary reactions in CH₄H₂O and CH₄CO₂ atmospheres were proposed to distinguish different physical and chemical processes within anodes. The results of this study can be conducive to a more precise understanding of reaction mechanism on SOFC anodes and meaningful for practical application of DIR-SOFCs.     

Microstructural evolution and microwave transmission/absorption transition in polymer-derived SiOC ceramics

Herein, we present the structural evolution of polymer-derived SiOC ceramics with the pyrolysis temperature and the corresponding change in their microwave dielectric properties. The structure of the SiOC ceramics pyrolyzed at a temperature lower than 1200 °C is amorphous, and the corresponding microwave complex permittivity is pretty low; thus, the ceramics exhibit wave transmission properties. The Structural arrangement of free carbon in the SiOC ceramics mainly happens in the temperature range of 1200 °C-1300 °C due to the separation from the Si–O–C network and graphitization, while the structural arrangement of the Si-based matrix mainly occurs in the range of 1300 °C-1400 °C owing to the separation of SiC₄ from the Si–O–C network to form nanocrystalline SiC. In pyrolysis temperature range of 1200 °C-1400 °C, the microwave permittivity of SiOC shows negligible change. At a pyrolysis temperature exceeding 1400 °C, the carbothermal reaction of free carbon and the Si–O backbone becomes significant, leading to the formation of crystalline SiC. The as-formed SiC and residual defective carbon improve the polarization loss of SiOC ceramics. In this case, the SiOC ceramics show significantly increased complex permittivity, exhibiting electromagnetic absorption characteristics. These characteristics promote the application of polymer-derived SiOC ceramics to high-temperature electromagnetic absorption materials.     

Advances in micro-mechanical modeling using a bonded-particle model and periodic homogenization within discrete element framework applied to heterogeneous ceramics

The Discrete Element Method (DEM) can account for microcracks initiations and propagations within the microstructure and their impact on the macroscopic properties of ceramics. Combing the DEM with the Periodic Homogenization (PH) allows working with a limited number of elements, thus facilitating the multiscale transition of the elastic properties of ceramics: from the microscale (inclusion/pores scale) to the macroscopic elastic behavior of such continuum media. However, the PH approach for a continuum media is currently less developed in DEM than the FEM. Hence, this study aims to consolidate a DEM framework, using a bonded-particle model and PH to improve the prediction of the elastic properties (Cij tensor) of ceramics. Here, a face-centered cubic unit cell is combining? with periodic boundary conditions to build a 3D representative volume element in DEM to model the macroscopic elastic properties of model materials and is validated by experimental data, analytical and FEM approaches.     

Electroxidation of sulfur slurries: Reaction rate studies

The rates of sulfur-assisted water electrolysis can be enhanced by addition of the redox-mediators of Fe²⁺, Ce⁴⁺, V⁵⁺ and Cl⁻. Another approach to enhancing the reaction rates lies in operating the electrolysis cell at higher temperature. The anticipated advantages of high temperature operation are: (i) increase in the rates of reaction; (ii) lowering of the polarization potentials (i.e. overpotentials); and (iii) lowering of the reversible (thermodynamic) cell potentials. The energy usage for H₂ production for sulfur-assisted water electrolysis is computed and compared with that for ordinary water electrolysis.     

Thermomechanical aspects of mixed friction in concentrated contacts

Important aspects of partial elastohydrodynamic lubrication are discussed. For heavily loaded counterformed machine parts such as cams and followers, gear teeth, and ball- and roller-bearing elements working in the mixed friction regime, thermomechanical effects on the micro scale have been investigated. The temperature distribution resulting from friction has been determined, assuming that an axially symmetrical source of heat occurs on the peak of the contacting asperity.The thermal deformations and stresses in interacting asperities are obtained with the finite element method. A statistical analysis of the thermomechanical quantities has been carried out. Conclusions about the temperatures and the thermal stresses in contacting asperities have been formulated. A thermoelastic coupling of the interacting rough surfaces has been proposed as a mechanism of the scuffing mode of failure in concentrated contacts.     

水性羟基丙烯酸树脂的制备与研究

以甲基丙烯酸甲酯(MMA)、苯乙烯(St)和丙烯酸丁酯(BA)等为主要单体,引入丙烯酸(AA)、丙烯酸羟基乙酯(HEA)与甲基丙烯酸异冰片酯(IBOMA)等作为功能单体,通过半连续溶液聚合工艺,最后加水分散制得水性羟基丙烯酸树脂。利用FT-IR、透光度、粘度分析研究了单体配比、引发剂(BPO)用量、温度、链转移剂(DDM)用量、功能单体用量等因素对树脂性能的影响。结果表明,当AA、HEA、IBOMA、BPO和DDM的质量分数分别为3%、12%、10%、3%和2%,聚合反应温度100℃时可获得粘度为5 Pa.s,固含量约45%的水性羟基丙烯酸树脂。